OF WASHINGTON. 123 



sion, may be frozen solid there would seem to be hardly any 

 limit to the continuation of this condition. Another interesting 

 fact, worth mentioning in this connection, is that when artificial 

 cold is brought to bear upon summer broods of chrysalides, the 

 effect is noticeable in the character of the resultant imago, sea 

 sonal dimorphism being in many ways directly attributable to 

 the influence of temperature. 



SUMMARY. 



From the above statement of the more salient facts on this 

 subject a superficial selection from the immense number that 

 might be cited certain conclusions are justified. In general, it 

 may be said that the great majority of insects, like annual plants, 

 have their individual lives limited by the year, and that the con 

 ditions that determine which of the four states egg, larva, pupa, 

 or imago shall occupy the longest period, are extremely difficult 

 to formulate. Temperature and food-supply undoubtedly influ 

 ence and control the length of the life-cycle ; for insects strikingly 

 exemplify the principle that the individual life is shortened in 

 proportion as its activities are accelerated, and lengthened ac 

 cording as these are inactive or dormant. But whether the 

 shortened or lengthened period of the normal or annual life- 

 cycle of the insect shall be in the egg, the larva, the pupa, or the 

 imago state, depends on conditions which we certainly cannot 

 formulate. All that we can say is that there is a correlation be 

 tween the protracted life in any one state and the more ephemeral 

 existence in the other states. Thus the great majority of annual 

 insects in the temperate zone hibernate in the larva state, which 

 covers, on the average, from one-half to three-fourths of the 

 year. But, as we have seen, the number of cases where the 

 dormant period is passed either in the egg, the pupa, or the 

 imago state, is very great, and hibernation in all these states takes 

 place not infrequently among species of the same family, of the 

 same genus, or even among individuals of the same species. 



These remarks remain essentially true for those species which 

 produce more than one annual generation. These not only hi 

 bernate in different states, according to the species, but there is 

 more or less irregularity in the same species, which may some 

 times hibernate in the imago, the pupa, the larva, or even in the 

 egg state. Even a portion of the same brood of larvae, hatching 

 from the eggs of a single parent, as we have just seen in Phvci- 

 odes, etc., may go into lethargy in midsummer and not transform 

 to the pupa state and give out the imago until the ensuing sum 

 mer, while the other portion will pass through their transforma 

 tions and continue their life functions the same year. 



